I don't like the idea of Fallout Online. A couple months after its release when the playerbase begins to grow large, it will ruin the feeling of the world having been torn apart by nuclear war. What little remained of the world's broken population scattered across the world and formed small pockets of civilization, desperately yet fruitlessly trying to grow. The drastically shortened life expectancy due to the many dangers of the nuclear wasteland kept the population sparse and isolated.
Then you throw in a million player characters. Suddenly it seems like Disney opened up a post-apocalyptic theme park.
It'd ruin the desperate solitude of wandering the wasteland.
The only fix for this is if they somehow made the game take place across the whole of America, a potentially memory-draining feat calling for a massive game world of 3,794,101 square miles.